Motorized vehicles include a power plant (e.g., engine or electric motor) that produces driving power. The driving power is transferred through a transmission to a driveline for driving a set of wheels at selected gear ratios. As is well known, automatic transmissions shift automatically to the appropriate gear ratio based on various vehicle operating conditions including speed and torque. Typically, a desired transmission operating mode or range is selected by the vehicle operator. The ranges provided by most automatic transmissions generally include Park, Neutral, Reverse and Drive. In Drive, the automatic transmission automatically shifts between three, four, five or even six different forward gear ratios based on the vehicle operating conditions.
Traditionally, a driver interface device is provided which the vehicle operator shifts to select the desired transmission range. The driver interface device may be linked to the automatic transmission by a range shift mechanism which may include a series of interconnected mechanical devices such as levers, push/pull rods, cables and the like. The number and size of such mechanical components make it difficult to package the range shift mechanism between the driver interface device and the transmission and can add significant frictional resistance to the overall system. As a result, the overall cost for design, manufacture and assembly of the vehicle is increased.
In an attempt to address such issues related to mechanically-shifted transmission range shift mechanisms, several electronic transmission range selection systems (ETRS) (also referred to as “shift-by-wire” range shift mechanisms) have been developed. Typically, an ETRS system includes an electric motor for controlling movement of the transmission's manual shaft to the desired range select position. Switches associated with a driver interface device send a mode signal to a transmission controller that is indicative of the selected transmission range. Thereafter, the controller actuates the electric motor to move the transmission manual shaft to the corresponding range select position.
To prevent the vehicle from inadvertently moving from an out-of-park condition to a park condition, a park inhibit solenoid assembly may be provided. One example of a park inhibit solenoid assembly is described in U.S. Patent Application Publication No. US 2004/0248687 A1, the teachings of which are incorporated herein by reference. Another example of a park inhibit solenoid assembly is shown in FIG. 1. The illustrated assembly includes a body portion 100 and a follower assembly 102. A solenoid 104 is energized to force a ball 106 into a notch 108 for locking the follower assembly 102 in an out-of-park position. If the solenoid 104 is de-energized, a ramp 112 on the follower pushes the ball 108 down to allow the solenoid move to the park position.
The illustrated assembly is difficult to manufacture. The body 100 may be machined or die cast with critical areas that require tight tolerance. The illustrated follower assembly 102 includes four parts; a cylindrical follower 110 with a ramp 112 machined at a prescribed location; a pin 114 positioned to ride in a slot in the body to limit travel; a hook 116 to engage with a park pawl; and a pin 118 for coupling the hook to the follower. The follower assembly 102 can be very costly to manufacture. Also, the ball 106 may be located in a pocket inside the body. Debris entering the pocket may prevent proper locking of the system. Moreover, the ball engages the follower at a specific location, leading to a potential for deformation. For example, an indentation may form at the point of contact between the ball and follower. The indentation may modify the intended direction of the force on the follower, thereby preventing proper operation of the system.
Accordingly, there is a need for a park inhibit solenoid assembly that is reliable and cost efficient in design.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the subject matter be viewed broadly.